Farmers in the United States operate over two million farms covering roughly one billion acres of land and producing hundreds of billions of dollars of crops each year. The farmers spend tens of billions of dollars per year on seeds, fertilizer, chemicals and fuel. A modern farm is a complex operation where precision and efficiency can have a significant impact on the bottom line. According to the USDA, the most efficient 25% of US corn growers spend about $1 to grow a bushel of corn while growers in the least efficient 25% spend $3 to grow the same amount.
One way farmers improve efficiency is by avoiding unnecessary overlaps in tilling, spraying and harvesting operations. In other words, they avoid driving their tractors and equipment over the same area twice. Consider an 80-acre field and a 44-foot wide sprayer towed behind a tractor as an example. The sprayer is towed across the field in series of overlapping tracks. If the overlap between adjacent sprayer tracks is reduced from two feet to four inches, then four acres of spraying are eliminated. Such precision may be achieved by guiding tractors with global positioning system (GPS) based steering systems.
Precision control of towed farm implements such as plows, rippers, disks, planters, applicators, drills and other equipment has other benefits as well. It makes it easier to operate machinery in dark or dusty conditions. Operators can drive faster and reduce driving stress. The quantity of fuel and chemicals used can be decreased, thereby saving money and the environment. Soil compaction can be avoided by keeping heavy equipment on precise tracks.
Advances in GPS technology (and systems based on other global navigational satellite systems (GNSS) such as the Russian GLONASS and the European GALILEO) have made it possible to drive large farm tractors along predetermined paths very accurately. A tractor can return to a field a year after first working it and follow the same track within an inch. Control of towed implements is more difficult, however.
A towed implement is attached to a tractor by a hitch and the tractor pulls the implement across the ground. The implement may wander off its intended path for any number of reasons including asymmetrical loading (e.g. tougher ground to plow on one side than the other) or drag due to operating on a slope. Skilled tractor operators can compensate for a wandering implement by deliberately steering the tractor away from a desired path so that the implement stays on the path even though the tractor does not. However, despite the best efforts of operators, this manual method is imprecise, takes a long time and travel distance, and causes operator fatigue.
“Automatic Control of Passive, Towed Implements” (U.S. patent application Ser. No. 12/244,198, filed on Oct. 2, 2008) describes systems and methods that guide towed implements along a desired path by directing an autopilot-controlled tractor optimally off the path. These and other feedback methods for controlling towed implements provide optimal reactions to disturbances. They decrease the response time required for an implement to execute a step offset from a predetermined path.
Despite the success of feedback control systems for towed implements, further improvements are possible. In particular, feedback control systems have not eliminated implement tracking errors that can occur on curved paths or changing slopes. What is needed are new systems and methods to ensure that towed implements follow their intended paths as accurately as possible even when those paths include curves, changing slopes or other known influences.